The present invention is directed to probe stations for making highly accurate measurements of high-speed, large scale integrated circuits at the wafer level, and of other electronic devices.
Such measurements require set-up and calibration steps using contact substrates and calibration substrates prior to and during the respective measurements. With most previous probe stations, the contact and calibration substrates, and the test wafer, cannot be mounted on a supporting chuck simultaneously, thus requiring repetitive time-consuming unloading and loading of the chuck between successive set-up, calibration, and measurement steps. In controlled-environment probe stations having hermetically-sealed enclosures for providing a dry environment for low-temperature testing, this problem is even worse because of the repetitive need to re-purge the enclosure with a dry gas and reestablish steady-state thermal conditions for each unloading and loading sequence.
These problems were partially alleviated with the introduction of the Summit 9000.TM. probe station, manufactured by Cascade Microtech, Inc. of Beaverton, Oreg., which featured a square wafer chuck having a central wafer-supporting surface area and separately vacuum-controlled corner surface areas for holding a calibration substrate and a contact substrate simultaneously with a wafer. However the integral nature of this square wafer chuck left several problems unsolved. The central wafer-supporting surface area of the chuck could not be replaced with different types of surfaces having different metal plating, impedance characteristics, or thermal characteristics without also replacing the corner surface areas, nor could the respective elevations of the respective wafer or substrate-supporting surfaces be adjusted with respect to each other to compensate for differences in thicknesses between contact, calibration and wafer substrates. Moreover the placement of the separate vacuum control valves, for controlling the corner surface areas, directly on the square wafer chuck made it impractical to use the chuck in conjunction with a controlled-environment enclosure isolating the surface areas from outside influences such as electromagnetic interference (EMI), moist air, and/or light, because the enclosure would inhibit access to the valves.